Conventional information processing devices utilize silicon-based technology which has certain known fundamental limitations when used to form integrated devices. Such devices are fabricated using a top down approach. In the microelectronics industry, for instance, lithographic techniques are used to etch away at a semiconducting (e.g. silicon) crystal or otherwise define deposited layers to form micrometer or even sub-micrometer size devices and circuitry. As device features have become finer, the number of devices that can be crammed onto a chip has been doubling approximately every 18 to 24 months for at least the last two decades. Smaller devices provide lower cost, higher speed and/or higher processing power. The vast majority of chips fabricated form digital devices, such as microprocessors, computers, memory devices and a wide variety of other related devices.
Digital technology can be explained with Boolean logic gates, such as NOT gates. The simplest of all gates is the NOT which functions as a simple inverter. The Not gate takes a single input signal and produces the opposite value as its output. Thus, true becomes false, and false becomes true. Boolean logic gates are devices that operate on signals with two possible values, such as true and false, or 1 and 0. An AND gate has two or more inputs and one output, the output being true only if all the inputs are true. An OR gate is similar except that the output is true if any of the inputs are true.
Chip makers will likely be unable to extend the current miniaturization trend for another decade. As features shrink into the several hundred nanometer range, chips will likely not be able to operate, or at least not operate reliably. Redundancy is generally not provided for integrated electronic devices, resulting in potential catastrophic failures in the field for entire integrated circuits due to a single isolated failures of discrete devices or a single connection between discrete devices. Connectivity of various discrete devices becomes increasingly problematic as device sizes have decreased. Moreover, the cost of constructing new fabrication lines for each new generation of chips is expected to become prohibitive. As a result, there is a need to develop alternative technologies for the fabrication computers and other integrated devices.
Organic molecules, including cellular molecules from living cells have been found to be generally resistant to a broad range of ambient and externally applied conditions and possess the potential to create information processing devices having high density levels without many of the above-mentioned limitations of silicon based technology. However, attempts to develop information processing capabilities based on organic molecules has had little success because many difficult challenges have been simultaneously encountered by researchers. For example, challenges arose in areas relating to stimulation of a plurality of molecules, detection of output signals generated by the molecules, as well as lack of design tools when utilizing such molecules analogous to computer aided design (CAD) which is commonly used to design electronic devices.
Some devices have incorporated the use of non-cellular organic molecular material in combination with electrical devices and systems. For example, International Application No. PCT/US00/01360 to the University of South Carolina, describes a nanocell molecular computer.
The described nanocell computer contains a two-dimensional array of a few hundred metallic nanoparticles bridged by a somewhat higher number of functional organic molecules. These functional molecules connect the nanoparticles to input and output leads arranged around the periphery of the nanocell. Thus, different combinations of input and output leads allows addressing different current-carrying pathways.
The arrangement of the nanoparticles and bridging molecules in these pathways is initially random. By applying voltage pulses to various combinations of input and output leads, molecules (switches) can be set to “on” or “off” states in groups. Which switches are on (conducting) and which are off (insulating) will not be initially known. In a trial-and-error fashion, computer algorithms repeatedly test and tinker with a pathway (using voltage pulses of different magnitudes) until the pathway performs the desired operation, such as that of a logic gate or adder. Thus, in view of the required programming of each switch, the teachings of the nanocell computer described by PCT/US00/01360 are not well suited for use in forming devices having any significant level of integration.
Another example of related technology is a biomolecular switching device called an enzyme transistor. Hiratsuka, M., T. Aoki, and T. Higuchi (1999) IEEE Trans. On Cir. and Sys. -I: Fund. Theory and Appl. 46 (2), 294–303 (Hiratsuka). The enzyme transistor described by Hiratsuka can be viewed as an artificial catalyst which selects a specific substrate molecule and chemically transforms it into a specific product. The catalytic activity of particular enzymes are each regulated by a specific effector.
The enzyme devices formed can be considered to be analogous to a bipolar junction transistor having a chemical substrate acting as an emitter, an enzyme acting as a base and a product acting as a collector. An integrated enzyme device can feature multiple enzyme devices which can be coupled together to form a network of biochemical reactions defined by the molecular selectivity of the enzyme transistors. Multiple enzyme transistors can be connected together by chemical diffusion, rather than a physical structure as in electronic integrated circuits for device-device interaction. Thus, wire-free computing circuits can be realized. The information is coded into molecular agents and then discriminated by the selectivity of the enzyme transistor. Hiratsuka describes formation of logic circuits, such as a NOR gate. Although Hiratsuka suggests the simple devices formed could be extended to more complex circuit designs, he provides little or no guidance in producing such devices.
Thus, available alternative devices such as the enzyme transistor proposed by Hiratsuka have not produced or cannot be expected to allow production of highly integrated information processing devices. Accordingly, the teachings of these available alternative devices are unable to approach or exceed integration levels offered by conventional silicon based devices which perform analogous functions.